The present invention relates to a variable-capacity swash-plate type compressor which is effective for use as a refrigerant compressor of an air conditioning system for automotive vehicles, for example.
In the prior application (U.S.A.: Ser. No. 147,036 on Jan. 20, 1988/CIP of Ser. No. 91,982 on Sep. 1, 1987), one of the inventors of this application and others have proposed that, in a swash-plate type compressor in which fluid is compressed within a pair of working chambers arranged respectively at opposite ends of each piston, an angle of inclination of a swash plate is varied while preventing a dead volume from increasing uniformly in each of the working chambers at the opposite ends of the piston, thereby controlling the capacity of the compressor continuously.
The swash-plate type compressor is arranged such that a spool is engaged with the swash plate rotatively driven by a shaft, and an angle of inclination of the swash-plate is reduced by axial movement of the spool, to alter the stroke of the piston. Further, the arrangement is such that a spherical bearing is arranged at the center of the swash plate, and is also displaced in synchronism with the spool. With such arrangement, while the dead volume increases considerably in one of the pair of working chambers, the capacity decreases gradually without being accompanied with a considerable increase of a dead volume in the other working chamber. Accordingly, the capacity of the compressor can be controlled continuously in compliance with displacement of the spool.
There may be a case in the swash-plate type compressor that the spool is not displaced well under the influence of a dead space produced in one of the pair of working chambers at the opposite ends of the piston, in a state in which an amount of decrease in the stroke of the piston is small, in other words, in a state in which the discharge capacity of the compressor decreases more or less from the maximum discharge capacity. By this reason, supplementing load means is provided for supplementing the displacement of the spool, thereby enabling the displacement of the spool to be controlled even if the displacement of the spool is in the state described above.
However, the above supplementing means requires a spring unit considerably high in spring constant, so that the design of the spring unit is difficult from the viewpoint of stress. Further, since the spring force is excessively strong in case of a low compression ratio, pressure of control fluid required to bring the capacity of the compressor to the maximum against the spring force exceeds the discharge pressure of the compressor. Thus, there may be a case where it is made difficult to secure the control fluid.